The overall objective of the Controlled Exposure Facility core is to provide capabilities for the study of human and animal toxicological responses to inhalation exposures of combustion-generated particles and gases. This core will primarily provide technical support, facilities, management and coordination of controlled exposure experiments for the toxicology and human clinical studies, and will also provide technical advice to the epidemiology project on characterization of atmospheric aerosols, exposure assessment of airborne particles and gases, and source/receptor relationships of ambient air pollutants. . The combustion exhaust exposures in support of the toxicology and human clinical studies will take place in a recently built and wellcharacterized exposure facility in the Northlake Laboratory of the University of Washington. This exposure generation and characterization activity will be achieved via the following specific aims: 1) Generate relevant combustion exhaust exposure atmospheres; 2: Characterize particles and gases generated during each exposure; 3) Modify exposure atmospheres to enhance understanding of the toxicity of diesel exhaust. These modifications will provide experimental conditions that permit experimental evaluation of toxicity to biological systems.